Field of the Invention
The present invention relates to an electrophotographic member, a process cartridge and an electrophotographic image forming apparatus.
Description of the Related Art
Electro-conductive members such as charging rollers, developing rollers, and transfer rollers are used in electrophotographic apparatuses, which are image forming apparatuses based on an electrophotographic method.
These electro-conductive members require their electrical resistance values to be controlled at 103 to 1010Ω without depending on use conditions and usage environments. In this respect, an electro-conductive member having an electro-conductive layer rendered electro-conductive using an ionic conductive agent such as a quaternary ammonium salt compound is known.
Such an ionic conductive agent may be oozed (hereinafter, this oozing is also referred to as “bleeding”) to the surface of the member with time or in a high-temperature and high-humidity environment. The ionic conductive agent thus oozed causes change in outer diameter dimension, stains on the surface of the member, deterioration in adhesive properties, and poor images resulting from the contamination of the surface of other members contacted therewith. In addition, the ionic conductive agent may be ionized into anion components and cation components due to electrification so that these ions are moved and thereby maldistributed, leading to reduction in electro-conductivity.
As a unit for suppressing the bleeding of the ionic conductive agent and reduction in electro-conductivity caused by electrification, Japanese Patent Application Laid-Open No. 2006-189894 discloses that a quaternary ammonium salt in which any one of 4 alkyl groups bonded to the nitrogen atom of the quaternary ammonium salt is an octyl group, and the remaining 3 groups are methyl groups is used as the ionic conductive agent. Use of this ionic conductive agent, even added in a small amount, can achieve the lowering of resistance and is therefore less likely to cause the bleeding of the ionic conductive agent to the surface.
According to the studies of the present inventors, however, the electro-conductive layer rendered electro-conductive using an ionic conductive agent is still desired to achieve higher levels of the control of the bleeding of the ionic conductive agent and time-dependent change in electro-conductivity.
Particularly, with the recent speed-up and enhanced minuteness of electrophotographic apparatuses, higher voltage is applied to electro-conductive members and thus tends to cause the bleeding of the ionic conductive agent and time-dependent change in electro-conductivity.